1. Field of the Invention
The present invention relates to a circuit breaker having an electrodynamically opening contact system for limiting current. The contact system has a fixed contact element and a contact arm (forming a movable contact element) movable into an off and on position by an operating shaft. There is further provided a spring which acts upon the contact arm through the intermediary of a force-transmitting lever. Further, the contact arm has a tripped position into which it is moved from the on position by an overloadresponsive device when the current flow through the circuit breaker is of excessive intensity.
2. Discussion of the Prior Art
Switches having electrodynamically opening contact systems are generally known in the prior art. In German Patent No. 1,079,176 two parallel mounted tension springs are arranged between a pin disposed transversely through the movable contact element and a fixed point in the vicinity of the fulcrum. In the closed contact position the two springs have a force component which generates a contact force on the movable contact element. As soon as the movable contact element opens in response to an electrodynamic force, the direction of the contact force is reversed.
Similar solutions are disclosed in British Patent No. 1,564,412 and U.S. Pat. No. 4,540,961. However, in U.S. Pat. No. 4,540,961 there is no displacement of the force component in the hold-open position; rather, this is effected by friction. European Patent No. 148,111 to which corresponds U.S. Pat. No. 4,562,419, discloses a tension or compression spring arrangement which has a displaceable point of engagement between limits of a slide guide.
In these prior art spring arrangements, the spring is either disposed very close to the fulcrum of the movable contact element or it is disposed at a more remote location. If the spring is disposed close to the fulcrum it must generate very great forces relative to the contact pressure. If the spring is disposed at a more remote location it must be able to function with very large pivot paths or deformations. For multi-pole circuit breakers, in which the movable contact elements are mounted in a common operating shaft, the stationary attachment point of the spring must also be located in the operating shaft.